The Facade in High-Rise Buildings
In general towers are exposed to its four sides generating a big fa?ade surface that needs to be solved in a situation where technical and functional requirements are extreme and, probably, curtain wall is no longer the best solution.
High-rise building fa?ades, even being exempted from assuming main structure loads, are still subject to considerable mechanical efforts due to the wind loads achieved at certain heights depending on the geographical localisation and climate. Wind load high values make difficult not only the fa?ade proper functioning: junction tightness, exterior elements fixing, windows opening and so on, but also the assembly process.
The main issue is building a fa?ade at a height where wind loads are much higher than usual. In the case of the Turning Torso building by Santiago Calatrava, we can see a clear example of an extreme wind exposition. The Turning Torso, in the Swedish city of Malmo, is an exempt tower of 180 m height built in a residential area next to the sea, where most of the buildings have around four floors. The mechanic action was quantified in a range between ±2.5 and ±4.5 kPa, 255 and 460 kg/m2 at the wind tunnel (Banco de montaje de modulos 2005). This load is conditioned, among other things, by the geometry of the receiver’s body, that is to say, this range of loads would be the ones acting over the finished tower. Even though, it is logical to think that during the construction process some wind gusts can originate wind loads of similar values. In this case, there would be some situations where it would be impossible to work on-site.
Big format components, either as panels with different claddings or as lightweight frames, have been widely used in high-rise buildings.
In 1951, Mies Van der Rohe used a big format frame grid-shaped to partially solve the fa?ade of Lake Shore Drive buildings, in Chicago. The frame was made with three steel I-shaped profiles connected by horizontal plates that redrew the slabs edges in the fa?ade. Each frame solved the fa?ade between two pillars and two floors high. The joint between pieces was positioned in front of the pillar and in the fraction between two floorings at approximately 1/3 of one of them. The frames allowed to reach the site with a fragment of fa?ade pre-assembled that, with very few assembly operations on-site solved a big fa?ade surface. The frames were raised before pouring concrete in the slabs made by prefabricated elements: steel beams and plates. Frames acted as lost formwork (Fig. 10.2) (Campi 2000).
Nowadays, frames systems live together with the unitised one: facade panels usually made with aluminium profiles and clad depending on the project needs. They are directly anchored to the main building structure. In this case, the fa?ade arrives to the site nearly finished, with only some final endings left in some cases. Other fa?ade types may have sense in less height towers.
The objectives are clear:
• To complete the fa?ade as soon as possible with the installation workers accessing from the floor slabs at all times, limiting the use of auxiliary resources and spending as little time as possible in an exposed situation.
Fig. 10.2 Exposed Fagade
- • To make use of the possibilities offered by the industry to customise mass- produced elements and systems, designing with constant contributions from the various professionals involved (Convergent Design) and the quality guarantees.
- • To limit and monitor the generation of loss or waste, that because it is not produced on the different floors of the tower but rather at the site where the frame or unitised module is assembled, in other words the workshop, are more easily managed.
While the unitised system clearly responds to the aforementioned objectives, the frames fagade still requires in situ work. Which is the advantage then? The usual unitised systems resolve the watertightness of the joints thanks to a triple plane sealing with a drainage chamber that is created when pressing the two panels at their butt joints (Fig. 10.3). In other words, the proper functioning of the joint depends on a pressure that must be exerted in parallel to the fagade plane. In contrast, the frames system is implemented by placing the cladding from the interior and the exterior over the frame, that is, the cladding can be secured by applying pressure over the frame perpendicular to the fagade plane. This pressure is easily increased when the climatic conditions worsen, improving the behaviour of the joint.
Going back to the example of Turning Torso, the company Folcra designed some unitised panels for this fagade that are fitted from the exterior, applying pressure over mullions that had been positioned previously. In other words, the system makes use of the advantages of the panel that is completely finished in the workshop and those provided by a frame that is fitted by applying pressure from the exterior (Fig. 10.4).
Fig. 10.3 On site panels fabrication to reduce excessive labor